Strata control technology and applications of non-pillar coal mining

Non-pillar coal mining has been developed and applied for more than 60 a in China coal mines.The research achievements on non-pillar coal mining methods,applicable conditions and strata control technology,such as entry retained along gob side,entry driven along gob side,cross mining over roadway,and entry arranged in gob area,are comprehensively analyzed. The main contents about entry retained along gob side are:various types associated with different coal mining systems，rock deformation and damage features,rock structure mechanical model and interaction between surrounding rock and support;the types and mechanical performances of basic support,enhanced support in entry and the support set along entry side;the rock destressing mechanism and techniques on blasting and hydraulic fracturing;the optimization of entry cross section and maintaining period;support design principles and safety technology for entry driven along gob side. In regard to entry driven along gob side,the patterns and design methods for slender coal pillar are discussed,the rock structure features,main affecting factors of rock deformation and surrounding rock control techniques are analyzed. The forms of non-pillar cross mining over roadway are introduced,and the effects of vertical distance from cross working face floor to roadway roof and horizontal distance from face edge to roadway on its deformation are explained.The entry layout patterns in gob area,including entry maintained and driven in gob are introduced,the stress fields and construction difficult points associated with these entries are discussed.Two study cases are introduced:the entry retained along gob side maintained by the combination of pumped concrete prop and hydraulic fracturing destressing in Hejiata coal mine in Shaanxi Province,another one controlled by pumped rebar concrete wall and hydraulic fracturing destressing with long horizontal boreholes in Yechuan coal mine in Shanxi Province,and the strata control effects of the entries retained along gob side are analyzed. Finally,the improvement suggestions and development direction for non pillar coal mining methods and strata control technology are put forward.